Field of the Invention
The present invention relates to wireless communication and, most particularly, to a D2D operation method performed by a UE in a wireless communication system and a UE using the same method.
Related Art
The International Telecommunication Union Radio communication sector (ITU-R) is carrying out a standardization process of International Mobile Telecommunication (IMT)-Advanced, which is a next generation mobile communication system developed after the 3rd generation mobile communication system. The IMT-Advanced seeks to achieve the goal of providing Internet Protocol (IP)-based multimedia service support at a data transmission rate of 1 Gbps in an immobile state and a low-speed mobile state, and 100 Mbps in a high-speed mobile state.
As a system standard satisfying the requirements of the IMT-Advanced, the 3rd Generation Partnership Project (3GPP) is preparing for LTE-Advanced (LTE-A), which corresponds to an enhanced version of the Long Term Evolution (LTE) that is based on the Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission schemes. The LTE-A is one of the most promising candidates for the IMT-Advanced.
Interest has recently been growing in the Device-to-Device (D2D) technology, wherein direct communication is carried out between devices. Most particularly, D2D is drawing attention as the communication technology being suitable for public safety network. Although the commercial communication network is quickly shifting to LTE, due to the problem of collision with the legacy communication standard and the issue of cost, the current public safety network is still mostly based on the 2G technology. Such gap between the communication technologies and demand for more enhanced services are now leading to efforts in seeking to enhance the public safety network.
In comparison with the commercial communication network, the public safety network has a higher service requirement condition (reliability and security), and, most particularly, even when the coverage of cellular communication does not reach or is unavailable, the public safety network still requires direct transmission and reception of signals between devices, i.e., D2D operation.
D2D operation may have diverse advantages in that it can perform signal transmission and reception between close-ranged devices. For example, a D2D user equipment (UE) may perform data communication at a high transmission rate and low latency. Moreover, the D2D operation may scatter (or distribute or disperse) traffic that is being concentrated to a base station. If the D2D UE performs the role of a relay station, this may also result in expanding the coverage of the base station.
In the related art, it was impossible for a D2D UE located within the coverage of a base station to relay data transmitted from the base station to another D2D UE, which is located outside of the coverage of the base station. Accordingly, in order to resolve the above-described problem, a method for relaying data transmitting from a base station, by a D2D UE located within the coverage of a base station, to a D2D UE located outside of the coverage of the base station will be provided. At this point, a UE within the coverage of the base station (i.e., in coverage) relaying data to a UE located outside of the coverage of the base station (i.e., out of coverage) is referred to as a D2D relay user equipment (UE) and may also be referred to as a ‘relay UE’. Also, a UE receiving data from a relay UE while being located outside of the coverage of the base station may be referred to as a D2D remote user equipment (UE) and may also be referred to as a ‘remote UE’.
Herein, in case the remote UE fails to select an adequate relay UE, it may be impossible for the remote UE to perform communication with the network. Accordingly, it is important for the remote UE to select an adequate relay UE and to perform communication with the base station through the selected relay UE.
Accordingly, a detailed description on a method of a remote UE for selecting a relay UE and a device using the same will hereinafter be provided.